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Assertion: Eukaryotic cells have the ability to adopt a variety of shapes and carry out directed movements.
 Reason: There are three principal types of protein filaments-actin filament, microtubules and intermediate filaments, which constitute the cytoskeleton.
  1. Assertion is true but Reason is false.
  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
  3. Both Assertion and Reason are false
  4. Both Assertion and Reason are true and Reason is the correct explanation of Assertion


Solution

The correct option is D Both Assertion and Reason are true and Reason is the correct explanation of Assertion
Eukaryotic cells (particularly) animal and lower plant cells) have the ability to adopt a veriety of shapes and carry out directed movements because they have a network of protein fibres that support the shape of the cell and anchor organelles to fixed location. This network is called cytoskeleton. Later is made up of actin filaments, which are made of two strands of the fibrous protein twisted together and usually occur in bundles.
(i) Actin Filaments are ubiquitous, and are concentrated below the plasma membrane in bundles known 
 as stress fibres, which may have a contractile function.
(ii) Microtubules, which are composed of 13 stacks of tubulin protein subunits arranged side by side to 
 form a tube. Microtubules are comparatively stiff cytoskeletal elements that serve to organize 
 metabolism and intracellular transport in the non-dividing cell.
(iii) Intermediate filaments, which are composed of overlapping staggered tetramers of protein. This 
 molecular arrangement allows for a rope-like structure that imparts tremendous mechanical 
 strength to the cell.

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